Battery pack

ABSTRACT

An apparatus includes a first cell subpack having a plurality of cells arranged in series and a second cell subpack connected in series to the first cell subpack. The second cell subpack includes a plurality of cells arranged in series and at least one cell arranged in parallel with one of the plurality of cells, arranged in series, of the second cell subpack, where the first cell subpack and the second cell subpack use a first voltage rail to provide at least a first voltage level and a second voltage rail to provide a second voltage level, where the first voltage level is different from the second voltage level.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/436,555, filed Jan. 26, 2011, entitled “Battery Pack,” which ishereby incorporated by reference in its entirety.

TECHNICAL FIELD

This description relates to a battery pack for a device.

BACKGROUND

A battery pack may be used to provide power to a mobile device and itsvarious different components or loads. The various different componentsor loads in a mobile device may have different voltage and/or powerrequirements. It may be desirable to provide a battery pack having anarchitecture to meet the different voltage and/or power requirements.

SUMMARY

According to one general aspect, an apparatus includes a first cellsubpack having a plurality of cells arranged in series and a second cellsubpack connected in series to the first cell subpack. The second cellsubpack includes a plurality of cells arranged in series and at leastone cell arranged in parallel with one of the plurality of cells,arranged in series, of the second cell subpack, where the first cellsubpack and the second cell subpack use a first voltage rail to provideat least a first voltage level and a second voltage rail to provide asecond voltage level, where the first voltage level is different fromthe second voltage level.

Implementations may include one or more of the following features. Forexample, the second cell subpack may include multiple cells arranged inparallel with one of the plurality of cells, arranged in series, of thesecond cell subpack and the cells arranged in parallel match each otherin battery chemistry and differ from each other in cell capacity. Thefirst voltage level may be matched to an expected first load voltagelevel and the second voltage level may be matched to an expected secondload voltage level.

In one exemplary implementation, the apparatus may further include afirst voltage regulator connected to the first cell subpack and thesecond cell subpack to regulate the first voltage level to match anexpected first load voltage level and a second voltage regulatorconnected to the first cell subpack and the second cell subpack toregulate the second voltage level to match an expected second loadvoltage level. The first voltage regulator may include a boost voltageregulator to regulate the first voltage level to match an expectedbacklight unit voltage level and the second voltage regulator mayinclude a buck voltage regulator to regulate the second voltage level tomatch an expected universal serial bus (USB) voltage level.

In one exemplary implementation, the apparatus may further include abalancer connected to the first cell subpack and the second cellsubpack, where the balancer is configured to shuttle charge from thefirst cell subpack to the second cell subpack.

The first cell subpack may provide the first voltage level and thesecond cell subpack may provide the second voltage level independent ofthe first cell subpack. The first cell subpack may be configured operatein an operating mode and, at a same time, the second cell subpack may beconfigured to operate in charging mode. A cell within the first cellsubpack may charge one or more other cells within the first cellsubpack. A cell within the first cell subpack may charge one or moreother cells within the second cell subpack.

In one exemplary implementation, the apparatus may further include athird cell subpack having a plurality of cells arranged in series and atleast one cell arranged in parallel with one of the plurality of cells,arranged in series, of the third subpack. The third cell subpack may beconnected in series to the first cell subpack and the second cellsubpack and may be configured to provide at least a third voltage level,where the third voltage level is different from the first voltage leveland the second voltage level. The apparatus may further include a firstbalancer connected to the first cell subpack to transfer charge amongthe cells within the first cell subpack, a second balancer connected tothe second cell subpack to transfer charge among the cells within thesecond cell subpack and a third balancer connected to the third cellsubpack to transfer charge among the cells within the third cellsubpack. The apparatus may further include a fourth balancer connectedto the first cell subpack, the second cell subpack and the third cellsubpack. The fourth balancer may be configured to transfer chargebetween the first cell subpack, the second cell subpack and the thirdcell subpack.

In another general aspect, an apparatus includes multiple cells arrangedin series, where the multiple cells are configured to provide a firstvoltage level to a first load through a first voltage rail, a voltageregulator connected to the first voltage rail, where the voltageregulator is charged by the multiple cells in series and at least onelithium ion cell connected to an output of the voltage regulator. Thelithium ion cell has a battery chemistry different from the multiplecells arranged in series, where the voltage regulator is configured tocharge the lithium ion cell.

Implementations may include one or more of the following features. Forexample, the lithium ion cell may be a lithium iron phosphate cell. Thevoltage regulator may be configured to charge the lithium ion cell onlyon demand at peak efficiency. The lithium ion cell may be configured toprovide a second voltage level to at least a second load through asecond voltage rail.

In another general aspect, an apparatus includes a first cell subpackhaving multiple matched cells in series to provide a first voltage leveland a second cell subpack connected in series to the second cellsubpack. The second cell subpack includes multiple unmatched cells inparallel to provide a second voltage level, where the first voltagelevel is different from the second voltage level and the unmatched cellsin parallel have a same cell chemistry.

Implementations may include one or more of the following features. Forexample, charge may be transferred between the first cell subpack andthe second cell subpack to recharge the second cell subpack from thefirst cell subpack. The first cell subpack may operate independent fromthe second cell subpack.

The details of one or more implementations are set forth in theaccompanying drawings and the description below. Other features will beapparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an exemplary battery pack.

FIG. 2 is a schematic diagram of an exemplary battery pack.

FIG. 3 is a schematic diagram of an exemplary battery pack.

FIG. 4 is a schematic diagram of an exemplary battery pack.

FIG. 5 is a schematic diagram of an exemplary battery pack.

FIG. 6 is a schematic diagram of an exemplary battery pack.

FIG. 7 is a schematic diagram of an exemplary battery pack.

FIG. 8 is a schematic diagram of an exemplary battery pack.

FIG. 9 is a schematic diagram of an exemplary battery pack.

DETAILED DESCRIPTION

In one general aspect, a battery pack architecture may include variouscombinations of series and parallel battery cells (also simply referredto as “cells”). The battery pack may include multiple taps or multiplevoltage rails that are arranged to provide different voltages to variousloads having different voltage and power requirements. In this manner,the arrangement of the cells and the voltage rails coming off of thecell terminals in the battery pack may be configured based on anexpected use of the rails to most efficiently meet the voltagerequirements of different loads (e.g., different loads in an electronicdevice). The number of cells used in the battery pack and theconfiguration of the cells and rails may be selected and arranged basedon an expected average use of the voltages by various different loads.In this manner, the battery pack may be isolated into varioussub-sections, where each of the sub-sections may provide differentvoltages for different loads.

The battery pack may be configured to provide multiple different voltagelevels, at the same time, to different portions of an electronic devicesuch as, for example, a tablet computing device, a laptop, a smartphone, or any mobile computing device. For example, one sub-section ofthe battery pack, including a certain configuration of cells from thepack, may provide one voltage level to power a backlight unit (“BLU”)and another sub-section of the battery pack, including a certainconfiguration of cells from the pack, may provide a different voltagelevel to power a universal serial bus (“USB”). Still other sub-sectionsmay provide different voltage levels to other components.

In one aspect, the battery pack may include an arrangement of cells inseries, where one or more of the cells in series may be arranged inparallel with other cells. In this manner, the cells arranged inparallel only need to match the battery chemistry of each other and donot need to match other aspects.

In one aspect, the cells and rails in the battery pack may be arrangedand configured based on the average expected use such that chargebalancing among the cells or the sub-sections would not be needed. Inthis situation, all of the cells or sub-sections in the battery packwould charge and discharge at the same rate such that charge balancingor cell balancing would not be needed.

In another aspect, where the cells in the battery pack may discharge andcharge at variable rates, then various cell balancing techniques may beused to shuttle charge from one or more cells to other cells. Forexample, in a battery pack where one configuration of cells provides ahigher voltage level to power a BLU, where the BLU was not draining muchpower, those cells having a higher state-of-charge (SOC) could be usedto charge other cells or groups of cells having a lower SOC in order toachieve cell balancing.

In the exemplary battery packs illustrated below, the voltage regulatorsand/or the cell balancing circuits may or may not be a part of thebattery packs. The battery packs may include the arrangement of cellsand the voltage rails or taps that may be used to connect directly toloads or to voltage regulators and/or cell balancing circuits. In someimplementations, those elements may be a part of the battery packs.

Various different cell balancing arrangements may be used in theexamples discussed below with respect to the figures. Although aparticular type of cell balancing arrangement may be illustrated, it isunderstood that other cell balancing schemes may be used such as, forexample, any-to-any isolated balancing, capacitor shuttle, single cellshuttle, etc.

Referring to FIG. 1, a schematic diagram illustrates an exemplarybattery pack 100 having ten (10) battery rechargeable cells 102, 104,106, 108, 110, 112, 120, 126, 128 and 130. For example, the cells mayinclude lithium ion (Li-ion), nickel cadmium (NiCd), or nickel metalhydride (NiMH) compositions with all 10 cells being of the same batterychemistry. The Li-ion cells may include an anode material such asgraphite and the cathode may be one of a layered oxide (e.g., lithiumcobalt oxide), a polyanion (e.g., lithium iron phosphate) or a spinel(e.g., lithium manganese oxide).

The example of FIG. 1 illustrates rechargeable cells having a Li-ioncomposition with each cell having a voltage range of about 3.0V fullydischarged to 4.2V fully charged.

Cells 102, 104, 106, 108, 110 and 112 may be arranged in series withcell 112 connected to ground 113. The cells 102-112 may provide avoltage input in the range of about 18V to 25.2V through a voltage railor tap 114 to a voltage regulator such as, for example, boost voltageregulator 116. The boost voltage regulator 116 may boost the voltageinput to a higher voltage such as, for example, to 50V. The output ofthe boost voltage regulator 116 may be configured to supply voltage to acomponent of a device such as, for example, a backlight unit (BLU),which may include multiple light emitting diodes (LEDs) 118 arranged ina desired configuration.

In the example of FIG. 1, the six (6) cells 102-112 arranged in seriesmay use approximately 60% of the overall battery pack 100 capacity. Inthis manner, approximately 60% of the overall battery pack 100 capacitymay be used to provide power to the BLU. While not illustrated, it isunderstood that battery pack 100 may include additional cells arrangedin series with the cells 102-112.

Cells 120 and 126 may provide an approximate voltage input of about 6Vto 8.4V through a voltage rail or tap 122 to a voltage regulator suchas, for example, buck voltage regulator 124. The buck voltage regulator124 may be configured to regulate the input voltage to a lower voltageoutput such as, for example, a 5V and/or a 3.3V voltage output. Theoutput of the buck voltage regulator 124 may be configured to supplyvoltage to one or more components of a device such as, for example, auniversal serial bus (USB) port. The USB port may be used, for example,to power and/or recharge devices plugged into the port.

Also, for the cells 110 and 120 arranged in parallel, the cells need notmatch each other with respect to shape, size, capacity, etc. It may onlybe necessary that the cells 110 and 120 match each other with respect tobattery chemistry. Furthermore, it is understood that other cells may beadded in parallel with these cells. While not illustrated, it isunderstood that the battery pack 100 may include additional cellsarranged in parallel with the cells 110 and 120.

In the example of FIG. 1, the two (2) cells 120 and 126 may useapproximately 20% of the overall battery pack 100 capacity. In thismanner, approximately 20% of the overall battery pack 100 capacity maybe used to provide power to the +5V and +3.3V regulators.

Cells 128 and 130 may provide an approximate voltage input of about 3.0Vto 4.2V through a voltage rail or tap 132 to a voltage regulator suchas, for example, buck voltage regulator 134. The buck voltage regulator134 may be configured to regulate the voltage input to a lower voltageoutput range such as, for example, a range of 0.9V to 2.5V. The outputof the buck voltage regulator 134 may be configured to supply voltage toone or more components of a device.

In the example of FIG. 1, the two cells 128 and 130 may useapproximately 20% of the overall battery pack 100 capacity. In thismanner, approximately 20% of the overall battery pack 100 capacity maybe used to provide a voltage input to the buck voltage regulator 134through the voltage rail 132.

Also, for the cells 112, 126, 128 and 130 arranged in parallel, thecells need not match each other with respect to shape, size, capacity,etc. It may only be necessary that the cells 112, 126, 128 and 130 matcheach other with respect to battery chemistry. Furthermore, it isunderstood that other cells may be added in parallel with these cells.

The voltage regulators 116, 124 and 134 may or may not be included aspart of the battery pack 100. Instead, the voltage regulators 116, 124and 134 may be components that are operably coupled to the battery pack100 through one or more terminals.

In an ideal situation, where the cells of the battery pack 100 alldischarge and charge together, it would not be necessary to perform anycell or charge balancing. In this manner, the cells would operate inlockstep. In this example, the cell count of ten (10) total cellsarranged in the illustrated series-parallel combination may be based onan average expected use of a device in which the battery pack may beused, including providing various different voltage levels through thevoltage rails 114, 122 and 132.

If the actual load ratio deviates from the ideal load ratio, then chargebalancing circuitry may be used to restore a balanced state of charge(SOC) to all of the cells. Different types of charge balancing circuitrymay be used including, for example, using current bypass techniques,charge redistribution techniques, any-to-any isolated balancing,capacitor shuttle, single cell shuttle, etc.

In one exemplary implementation, any of the three voltage rails 114, 122and 132 may be used to fully charge the battery pack 100. For example, acharger (e.g., wall charger), which is not illustrated in FIG. 1, may beused to charge the battery pack 100 to a certain % of capacity via afloat voltage applied to the rail 114. The remaining percentage of thecapacity may be provided using a charge balancing circuit (not shown) todistribute charge from the cell 102 and/or cells 104, 106 and 108 to thecells arranged in parallel, that is cells 110 and 120 and cells 112,126, 128 and 130.

Alternatively, for example, a 5V USB host supply may use the voltagerail 132 to charge the battery pack 100 to a certain % of capacity via afloat voltage applied to the rail 132. The remaining cells can bebrought to full capacity by the charge balancing circuit.

The battery pack 100 may be configured to operate in several differentmodes, some or all of which may be in operation simultaneously. Theoperating modes may include operating, charging and balancing. In oneimplementation, the cells may be grouped into sub-sections andindependently power their respective loads. For example, in theoperating mode, the cells 102-112 arranged in series may independentlypower the boost voltage regulator 116, the cells 120 and 126 mayindependently power the buck voltage regulator 124 and the cells 128 and130 may independently power the buck voltage regulator 134.

In the charging mode, the sub-sections of cells may be independentlycharged using the respective voltage rails 114, 122 and 132. In thebalancing mode, each of the sub-sections may include its own respectivebalancing circuit, which may be coupled or connected to the othersub-sections to enable cell balancing among the sub-sections. Differentcell balancing schemes may be used.

In this manner, while one sub-section is in one mode, the othersub-sections may be in different modes. For instance, one sub-sectionmay be in an operating mode, another sub-section may be in a chargingmode and another sub-section may be in a cell-balancing mode. Variouscombinations of the different modes and different sub-sections may berealized. Each of the sub-sections of various cell arrangements may beisolated from one another within the same battery pack 100. The isolatedsub-sections may be interconnected to enable the operation of thevarious modes.

While in many cases, all of the cells in sub-sections may be of theidentical type, this may not be necessary. Typically, all of the cellsin a series sub-system (also may be referred to as a “sub-pack”) may bematched. But the cells in the parallel sub-pack can have a differenttype and capacity. In fact, while the cells in a parallel sub-pack musthave identical battery chemistry, the cells in the parallel sub-pack mayinclude a variety of different cell constructions and capacities. Thiscapability may allow unique design approaches that are not possible withconventional battery pack construction.

In one exemplary implementation, a “lazy charging” scheme may be used.For example, a single, low-capacity “partner” cell within anintermediate (40-60% TYP) SOC range may be used. The partner cell maydraw charge from a cell having the highest voltage. The partner cell maydraw charge until either the highest voltage cell is adequately close tothat of the other cells or to the partner cell rises to a certain SOCsuch as, for example, 60% SOC. Then, the partner cell may dump chargeinto the series cell with the lowest voltage until either its voltage isadequately close to that of the other cells or the partner cell falls toa certain SOC.

In another exemplary implementation, the partner cell may be arranged toprovide the source for a system supply voltage rail (e.g., RTC, DRAMrefresh, sleep current, etc.). In another exemplary implementation, apartner cell may not be included and current withdrawn from series cellsby a balancing circuit is directly utilized by some system supply rail.In another exemplary implementation, cell balancing may be achieved bysupplying charge from a low-grade source such as, for example, a solarcell, to the weakest cell in a series chain of cells.

While FIG. 1 illustrates a battery pack 100 having 10 cells arranged inan unbalanced series-parallel combination having multiple taps toprovide output voltages to different loads, it is understood that othernumbers of cells and combinations of cells may be used to providemultiple different voltages using different taps or voltage rails toprovide output voltages to different loads of a device or devices.

Referring to FIG. 2, a schematic diagram illustrates an exemplarybattery pack 200. Battery pack 200 may include four (4) cells 202, 204,206 and 208. Cells 202, 204 and 206 may be arranged in series and cells204 and 208 may be arranged in parallel with respect to ground 210.

In the example of FIG. 2, the cells 202, 204 and 206 arranged in seriesmay provide a voltage input to a backlight unit (BLU) 212 throughvoltage rails (or taps) 214 and 216. The BLU 212 may be a voltageregulator which receives the voltage input and provides the desiredvoltage output to power multiple light emitting diodes (LEDs) 218 in adevice in which the battery pack 200 is being used. BLU 212 also may bereferred to as a LED boost controller.

The location of the ground 210 allows a conventional single-cellnegative ground architecture for the standard +5V, +3.3V, etc. rails,while allowing only one hop from either the top cell 202 or the bottomcell 206 to the center cells. The location of the ground 210 also allowsa higher voltage and supplies (e.g., +40V and −40V) to the LED BLUsupply, without exceeding regulatory limits of about 50V to ground.

The cells 204 and 208 may be configured in parallel and may provide avoltage input to supply voltage to any remaining loads of the device inwhich the battery pack 200 is being used. For example, the cells 204 and208 may provide a voltage input to a voltage regulator 220 throughvoltage rails 222 and 224. The voltage regulator 220 may be acombination of voltage regulators (boost, buck, buck/boost) to providethe desired voltage output to power loads having different voltagerequirements.

The battery pack 200 of FIG. 2 may exhibit that same or similarcharacteristics as battery pack 100 of FIG. 1, as described above.Additionally, for cell charging or cell balancing purposes, cells 202and 206, either alone or in combination, may be used balance the cells204 and 208. For example, cells 202 and 206, either alone or incombination, may be used to shuttle charge to cells 204 and 208. In thisexample, 75% of cell capacity may be used for the BLU 212 and theremaining 25% of capacity may be used for the other loads, without theneed for balancing circuits.

Referring to FIG. 3, a schematic diagram illustrates an exemplarybattery pack 300. Battery pack 300 may include the same cell arrangementas battery pack 200 of FIG. 2. Thus, battery pack 300 may include four(4) cells 202, 204, 206 and 208. Cells 202, 204 and 206 may be arrangedin series and cells 204 and 208 may be arranged in parallel with respectto ground 210.

In the example of FIG. 3, a separate voltage regulator 329 may beconnected to the circuit through rail 330 to use the voltage input ofthe cell 202 to power loads in a device in which the battery pack 300 isbeing used. For example, the voltage regulator 329 may provide voltageoutputs of 5V and 3.3V.

A voltage regulator 320 may be a buck voltage regulator and may use thevoltage input from cells 204 and 208 to provide a voltage output topower loads in the device in which the battery pack 300 is being used.In this exemplary implementation, some charge balancing schemes may needto use multiple hops when transferring charge from cell 206 to cell 202.

Referring to FIG. 4, a schematic diagram illustrates an exemplarybattery pack 400. Battery pack 400 may include four (4) cells 402, 404,406 and 408 with respect to ground 410. Cells 402 and 404 may be inparallel and cells 406 and 408 may be in parallel. Cells 402 and 404 maybe considered one sub-pack that is arranged in series with anothersub-pack of cells 406 and 408. Voltage rails or taps 412 and 414 mayprovide points for connecting the battery pack to output variousdifferent voltages to supply voltages to loads connected to the batterypack using, for example, buck voltage regulators 416 and 418.

Referring to FIG. 5, a schematic diagram illustrates an exemplarybattery pack 500. Battery pack 500 may include multiple cells 502 a, 502b through 502 n arranged in series. In one exemplary implementation, thecells 502 a-502 n may include from three (3) cells to nine (9) cellsarranged in series. In other exemplary implementations, other numbers ofcells may be arranged in series. In one exemplary implementation, thecells 502 a-502 n all may include the same battery chemistry such as,for example, including lithium cobalt oxide constructed cells.

The cells 502 a-502 n may provide a voltage input to a voltage regulator504 via a voltage rail (or tap) 506. In one exemplary implementation,the voltage regulator 504 may include a boost voltage regulator andboost the voltage input to the voltage regulator 504 to a voltage outputof approximately 60V. In other exemplary implementations, the voltageregulator may boost the voltage input to other voltage levels, includingvoltage levels greater than 60V. The voltage output may provide avoltage to a load in a device such as, for example, a BLU.

The cells 502 a-502 n also may provide a voltage input to a voltageregulator 508 via the voltage rail 506. In one exemplary implementation,the voltage regulator 508 may include a buck voltage regulator andprovide a voltage output of approximately 5V at 2 A. The voltage outputmay provide a voltage to a load in a device such as a USB port, whichmay supply power to or recharge devices connected to the USB port.

The cells 502 a-502 n also may provide a voltage input to a voltageregulator 510 via the voltage rail 506. The voltage regulator 510 mayregulate the input voltage to an output voltage range of about 3.15V to3.3V. In one exemplary implementation, the voltage regulator 510 may beconfigured as a charger to charge cell 512. The voltage regulator 510may be referred to as a smart charger or a peak efficiency charger sinceit may be configured to only run at over the narrow range of conditionswhere it is most efficient. In one exemplary implementation, the outputvoltage range may be 3.0V to 3.6V to allow for a +/−10% tolerance. Anarrower range may be selected based on the requirements of a particularsystem. For example, the charging may be started at 3.15V and stopped at3.3V.

The cell 512 may be a Li-ion cell having a different battery chemistrythan cells 502 a-502 n. For example, cell 512 may be constructed usinglithium iron phosphate (e.g., LiFePO₄). A lithium iron phosphateconstructed cell may be desirable due to its inherent properties of alow impedance and low voltage in the range of about 3.0V to 3.6V. Thevoltage input from the cells 502 a-502 n may charge the voltageregulator 510, which may run only on demand at peak efficiency to chargecell 512 when needed. In this manner, the voltage regulator 510 mayautomatically switch on and switch off as needed to charge cell 512. Thevoltage regulator 510 may periodically charge the cell 512 only when theregulator can be run at peak efficiency.

The cell 512 may be used to provide voltage inputs to voltage regulators516, 518, 520 and 522 via voltage rail 514. The cell 512 also may beused to provide a direct 3.15V-3.3V output without using a voltageregulator to provide voltage to any load requiring 3.3V. The voltageregulators 516, 518, 520 and 522 may include buck, boost or buck/boostvoltage regulators to provide the desired voltage outputs as indicatedin FIG. 5. The voltage output from the voltage regulators 516, 518, 520and 522 may provide voltage to any load requiring the indicated voltage.In this manner, the single cell 512 may be used to supply all of thelower supply voltage loads connected to the battery pack 500. Thevoltage from the cell 512 can directly supply the 3.15V-3.3V and canalso be regulated down using the voltage regulators 516, 518, 520 and522 to supply other low voltage loads.

In one exemplary implementation, an “emergency catch” regulator may beincluded and may be set at about 3.05V to assure that the systemsurvives a voltage spike. It may be a linear regulator or an on-off FETthat ensures that the rail does not dip below 3.0V.

For maximum capacity (mAh or Wh), a LiFePO4 cell (e.g., cell 512) istypically be charged to ˜3.6V, which also happens to be the upper limitfor a 3.3V+/−10% power supply. When the battery pack 500 is charged fromthe AC mains, the cell 512 will be fully charged to ˜3.6V. When placedin service, the cell 512 will initially be allowed to discharge as itsupplies power to its circuits. When the cell 512 reaches some lowervoltage such as, for example 3.25V, it will be charged from other cellsin the system at a rate that optimizes overall power system efficiency.Under light load, this overall charge rate will be determined byminimizing the product of the charger conversion efficiency and the cellcharging efficiency. Under heavy load, a higher charge current will berequired to avoid cell depletion. Charging will cease when the cell 512reaches some higher voltage such as, for example 3.35V. The process willrepeat cyclically until all cells in the system have fully discharged.Note that dynamic power in a CMOS circuit is proportional to V², sothere is a significant benefit to reducing the cell float voltage as lowas possible, limited only by the 3.0V MIN limit, the cell impedance andthe anticipated maximum load. For example, if the cell impedance is0.050 ohms, and the maximum load is 2 A, in the limit, the float voltagecould be set as low as 3.0+0.05*2=3.1V.

While not illustrated in FIG. 5, one or more cell balancers, includingcell balancing circuitry, may be connected to cells 502 a-502 n toshuttle charge between the cells in an efficient manner.

Referring to FIG. 6, a schematic diagram illustrates an exemplarybattery pack 600. The battery pack 600 may include multiple cellsarranged in series, with some of the cells in series also arranged inparallel with other cells. In one exemplary implementation, the batterypack 600 includes 15 cells. The battery pack 600 includes nine (9) cells602 a-602 i connected in series and configured to provide a voltagerange of about 27V to 37.8V, depending on the SOC of each cell beingbetween 3.0V and 4.2V. The cells 602 a-602 i may provide the voltagedirectly to a load or may provide the voltage as an input to a voltageregulator (not shown) via a voltage rail (or tap) 603.

The cells 602 a-602 i may be grouped in three groups of three cellseach, where each group of 3 may be connected to a respective cellbalancing circuit (also referred to as a balancer) 604, 606 or 608. Thefirst group of cells 602 a-602 c may be connected to balancer 604. Thebalancer 604 may be configured to use any one of a number of cellbalancing techniques to transfer charge among the cells 602 a-602 c. Thebalancer 604 may be used to account for and rectify minor differentialsin the state of charge between the cells in the first group due to, forinstance, differential aging of the cells or differences inmanufacturing. For example, the balancer 604 may efficiently transfercharge between 602 a and 602 b and between 602 b and 602 c.

The second group of cells 602 d-602 f may be connected to balancer 606.The balancer 606 may be configured to use any one of a number of cellbalancing techniques to transfer charge among the cells 602 d-602 f. Thebalancer 606 may be used to account for and rectify minor differentialsin the state of charge between the cells in the first group. Forexample, the balancer 606 may efficiently transfer charge between 602 dand 602 e and between 602 e and 602 f.

The third group of cells 602 g-602 i may be connected to balancer 608.The balancer 608 may be configured to use any one of a number of cellbalancing techniques to transfer charge among the cells 602 g-602 i. Thebalancer 608 may be used to account for and rectify minor differentialsin the state of charge between the cells in the first group. Forexample, the balancer 608 may efficiently transfer charge between 602 gand 602 h and between 602 h and 602 i.

The battery pack 600 also may include a balancer 610, which may beconfigured to transfer charge between the groups of cells. For example,the balancer 610 may be configured to transfer charge efficientlybetween the first group of cells 602 a-602 c and the second group ofcells 602 d-602 f and between the second group of cells 602 d-602 f andthe third group of cells 602 g-602 i. In some exemplary implementations,one or more of the balancers 604, 606 and 608 may be optional. The cellbalancers 604, 606, 608 and 610 of FIG. 6 may be used in other batterypacks illustrated and described in this document including, for example,battery pack 500 of FIG. 5.

The battery pack 600 also includes cells connected in parallel with someof the cells connected in series. For example, cell 602 g may beconnected in parallel to a cell 612 and may provide a voltage ofapproximately 9V to 12.6V via a voltage rail 614. The cells 602 g and612 may provide the voltage directly to a load or may provide thevoltage as an input to a voltage regulator (not shown).

Cell 602 h may be connected in parallel to a cell 616 and a cell 618 andmay provide a voltage of approximately 6V to 8.4V via a voltage rail620. The cells 602 h, 616 and 618 may provide the voltage directly to aload or may provide the voltage as an input to a voltage regulator (notshown).

Cell 602 i may be connected in parallel to cells 622, 624 and 626 andmay provide a voltage of approximately 3V to 4.2V via a voltage rail628. The cells 602 i, 622, 624 and 626 may provide the voltage directlyto a load or may provide the voltage as an input to a voltage regulator(not shown).

In addition to being configured to transfer charge between the cells 602g-602 i connected in series, the balancer 608 may be configured totransfer charge between cells, as needed, that are connected in parallelto the cells 602 g, 602 h and 602 i, respectively.

Referring to FIG. 7, a schematic diagram illustrates an exemplarybattery pack 700. The battery pack 700 may include three (3) cells 702,704 and 706 connected in series and one (1) cell 708 connected inparallel to cell 704 with respect to ground 710. Battery pack 700illustrates an efficiently balanced nominal 11.1V battery pack. Whilenot illustrated, a balancer may be connected to the cells 702, 704 and706 to efficiently transfer charges between the cells.

The cells 702, 704 and 706 may be configured to provide a voltage inputto voltage regulator 712, voltage regulator 714 and voltage regulator716 via a voltage rail 718. The voltages regulators 712, 714 and 716 mayprovide voltage outputs to loads of 60V (or more), 5V and 3.3V,respectively.

The cells 704 and 708 connected in parallel may be configured to providea voltage input to a voltage regulator 720 and voltage regulator 722 viaa voltage rail 724. The voltage regulators 720 and 722 may be configuredto provide voltage outputs to loads of 3.3V and 2.5V, respectively.

In the battery pack 700, it may be advantageous to run all of the loadsoff of the cells 704 and 708, except a BLU. Thus, the voltage regulator714 supplying the 5V may be moved to come off of voltage rail 724instead of voltage rail 718 and become a boost regulator instead of abuck regulator. In this manner, the top cell 702 and the bottom cell 706are more likely to remain in balance without having to use a balancer totransfer charge between the top cell 702 and the bottom cell 706.

Also, in this example battery pack 700, the cells are never more thanone hop away from transferring charge to another cell. For example,charge may be transferred between the top cell 702 and the two middlecells 704 and 708 in one hop and between the bottom cell 706 and the twomiddle cells 704 and 708 in one hop, which makes for more efficientcharge transfer, assuming charge balancing circuits are included, forexample, in a manner similar to FIG. 6.

Referring to FIG. 8, a schematic diagram illustrates an exemplarybattery pack 800. The battery pack 800 includes five (5) cells 802, 804,806, 808 and 810 connected in series and one or more cells 812 connectedin parallel to the cell 806, all with respect to ground 814. In thisarrangement, the cells 802, 804, 806, 808 and 810 connected in seriesmay provide a differential voltage between voltage rails 816 and 818 inthe approximate range of about 15V to 21V. This voltage may be used topower a load directly such as, for example, a BLU. These cells connectedin series also may provide a voltage input to a voltage regulator 820,which may be a buck voltage regulator to provide a voltage output of 5V.

In one exemplary implementation, the cells 806 and 812 connected inparallel may include cells constructed of lithium iron phosphate, asdescribed above with respect to cell 512 of FIG. 5. The cells 806 and812 connected in parallel may be configured to provide a voltage outputof 2.5V to 3.7V to a load, either directly or through a voltageregulator (not shown). The cells 806 and 812 may be any type of cell andvoltage. For example, if lithium iron phosphate cells are used, thevoltage range may be 2.5V-3.7V, if there are regulators, or the voltagerange may be 3.0V-3.6V if directly supplying a 3.3V rail.

The battery pack 800 also includes a balancer 822. The balancer 822 maybe configured to transfer charge between the cells. For example, thecells 802 and 804 may be considered a first group of cells, the cells806 and 812 may be considered a second group of cells and the cells 808and 810 may be considered a third group of cells. The balancer 822 maybe configured to efficiently transfer charge between the cell groups.For example, the balancer 822 may transfer charge efficiently betweenthe first group and the second group and between the second group andthe third group.

In one exemplary implementation, the balancer 822 may include a boostregulator for the situation where charge is transferred from the secondgroup of cells to either the first group of cells or the third group ofcells.

In another exemplary implementation, the battery pack 800 may include asixth cell (not shown) connected in series to the cell 806 as part ofthe second group of cells. In this implementation, the balancer 822 maynot need to include a boost regulator to transfer charge from the secondgroup of cells to either the first group of cells or the third group ofcells.

Referring to FIG. 9, a schematic diagram illustrates an exemplarybattery pack 900. The battery pack 900 includes seven (7) cells 902,904, 906, 908, 910, 912 and 914 connected in series and one or morecells 916 connected in parallel to the cell 908, all with respect toground 918. In this arrangement, the cells 902, 904, 906, 908, 910, 912and 914 connected in series may provide a differential voltage betweenvoltage rails 920 and 922 in the approximate range of about 21V to29.4V. This voltage may be used to power a load directly such as, forexample, a BLU.

In one exemplary implementation, the cells 908 and 916 and optionally,additional cells between 908 and 916, connected in parallel may includecells constructed of lithium iron phosphate, as described above withrespect to cell 512 of FIG. 5 to directly provide a 3.3V rail.Alternatively, with conventional 3-4.2V cells, the cells 908 and 916connected in parallel may be configured to provide a voltage output of3V to 4.2V to a load, either directly or through a voltage regulator(not shown).

The cells of the battery pack 900 may be configured in groups with afirst group of cells including cells 902, 904 and 906, a second group ofcells including cells 908 and 916, and a third group of cells includingcells 910, 912 and 914. The battery pack 900 may include a balancer 924to balance the charge within the first group of cells 902, 904 and 906.The battery pack 900 may include a balancer 926 to balance the chargewithin the third group of cells 910, 912 and 914.

The battery pack 900 also may include a balancer 928 to balance chargeamong the groups of cells. In this exemplary implementation, thebalancer 928 may likely only need to transfer charge from either thefirst group of cells 902, 904 and 906 or the third group of cells 910,912 and 914 to the second group of cells 908 and 916. In this manner,the balancer 928 may require buck only operation. The arrangement ofcells in the groups with respect to one another may result in the needto transfer charge in only one direction such that the balancer 928 canbe simplified to either a buck only or a boost only operation.

Implementations of the various techniques described herein may beimplemented in digital electronic circuitry, or in computer hardware,firmware, software, or in combinations of them. Implementations may beimplemented as a computer program product, i.e., a computer programtangibly embodied in an information carrier, e.g., in a machine-readablestorage device, for execution by, or to control the operation of, dataprocessing apparatus, e.g., a programmable processor, a computer, ormultiple computers. A computer program, such as the computer program(s)described above, can be written in any form of programming language,including compiled or interpreted languages, and can be deployed in anyform, including as a stand-alone program or as a module, component,subroutine, or other unit suitable for use in a computing environment. Acomputer program can be deployed to be executed on one computer or onmultiple computers at one site or distributed across multiple sites andinterconnected by a communication network.

Method steps may be performed by one or more programmable processorsexecuting a computer program to perform functions by operating on inputdata and generating output. Method steps also may be performed by, andan apparatus may be implemented as, special purpose logic circuitry,e.g., an FPGA (field programmable gate array) or an ASIC(application-specific integrated circuit).

Processors suitable for the execution of a computer program include, byway of example, both general and special purpose microprocessors, andany one or more processors of any kind of digital computer. Generally, aprocessor will receive instructions and data from a read-only memory ora random access memory or both. Elements of a computer may include atleast one processor for executing instructions and one or more memorydevices for storing instructions and data. Generally, a computer alsomay include, or be operatively coupled to receive data from or transferdata to, or both, one or more mass storage devices for storing data,e.g., magnetic, magneto-optical disks, or optical disks. Informationcarriers suitable for embodying computer program instructions and datainclude all forms of non-volatile memory, including by way of examplesemiconductor memory devices, e.g., EPROM, EEPROM, and flash memorydevices; magnetic disks, e.g., internal hard disks or removable disks;magneto-optical disks; and CD-ROM and DVD-ROM disks. The processor andthe memory may be supplemented by, or incorporated in special purposelogic circuitry.

To provide for interaction with a user, implementations may beimplemented on a computer having a display device, e.g., a cathode raytube (CRT) or liquid crystal display (LCD) monitor, for displayinginformation to the user and a keyboard and a pointing device, e.g., amouse or a trackball, by which the user can provide input to thecomputer. Other kinds of devices can be used to provide for interactionwith a user as well; for example, feedback provided to the user can beany form of sensory feedback, e.g., visual feedback, auditory feedback,or tactile feedback; and input from the user can be received in anyform, including acoustic, speech, or tactile input.

Implementations may be implemented in a computing system that includes aback-end component, e.g., as a data server, or that includes amiddleware component, e.g., an application server, or that includes afront-end component, e.g., a client computer having a graphical userinterface or a Web browser through which a user can interact with animplementation, or any combination of such back-end, middleware, orfront-end components. Components may be interconnected by any form ormedium of digital data communication, e.g., a communication network.Examples of communication networks include a local area network (LAN)and a wide area network (WAN), e.g., the Internet.

While certain features of the described implementations have beenillustrated as described herein, many modifications, substitutions,changes and equivalents will now occur to those skilled in the art. Itis, therefore, to be understood that the appended claims are intended tocover all such modifications and changes as fall within the scope of theembodiments.

1. An apparatus, comprising: a first cell subpack including a pluralityof cells arranged in series; and a second cell subpack connected inseries to the first cell subpack, the second cell subpack including aplurality of cells arranged in series and at least one cell arranged inparallel with one of the plurality of cells, arranged in series, of thesecond cell subpack, wherein the first cell subpack and the second cellsubpack use a first voltage rail to provide at least a first voltagelevel and a second voltage rail to provide a second voltage level,wherein the first voltage level is different from the second voltagelevel.
 2. The apparatus of claim 1 wherein the second cell subpackincludes multiple cells arranged in parallel with one of the pluralityof cells, arranged in series, of the second cell subpack and the cellsarranged in parallel match each other in battery chemistry and differfrom each other in cell capacity.
 3. The apparatus of claim 1 whereinthe first voltage level is matched to an expected first load voltagelevel and the second voltage level is matched to an expected second loadvoltage level.
 4. The apparatus of claim 1 further comprising: a firstvoltage regulator connected to the first cell subpack and the secondcell subpack to regulate the first voltage level to match an expectedfirst load voltage level; and a second voltage regulator connected tothe first cell subpack and the second cell subpack to regulate thesecond voltage level to match an expected second load voltage level. 5.The apparatus of claim 4 wherein: the first voltage regulator comprisesa boost voltage regulator to regulate the first voltage level to matchan expected backlight unit voltage level; and the second voltageregulator comprises a buck voltage regulator to regulate the secondvoltage level to match an expected universal serial bus (USB) voltagelevel.
 6. The apparatus of claim 1 further comprising a balancerconnected to the first cell subpack and the second cell subpack, thebalancer configured to shuttle charge from the first cell subpack to thesecond cell subpack.
 7. The apparatus of claim 1 wherein the first cellsubpack provides the first voltage level and the second cell subpackprovides the second voltage level independent of the first cell subpack.8. The apparatus of claim 1 wherein the first cell subpack is configuredoperate in an operating mode and, at a same time, the second cellsubpack is configured to operate in charging mode.
 9. The apparatus ofclaim 1 wherein a cell within the first cell subpack charges one or moreother cells within the first cell subpack.
 10. The apparatus of claim 1wherein a cell within the first cell subpack charges one or more othercells within the second cell subpack.
 11. The apparatus of claim 1further comprising a third cell subpack having a plurality of cellsarranged in series and at least one cell arranged in parallel with oneof the plurality of cells, arranged in series, of the third subpack,wherein the third cell subpack is connected in series to the first cellsubpack and the second cell subpack and is configured to provide atleast a third voltage level, wherein the third voltage level isdifferent from the first voltage level and the second voltage level. 12.The apparatus of claim 11 further comprising: a first balancer connectedto the first cell subpack to transfer charge among the cells within thefirst cell subpack; a second balancer connected to the second cellsubpack to transfer charge among the cells within the second cellsubpack; and a third balancer connected to the third cell subpack totransfer charge among the cells within the third cell subpack.
 13. Theapparatus of claim 12 further comprising a fourth balancer connected tothe first cell subpack, the second cell subpack and the third cellsubpack, the fourth balancer configured to transfer charge between thefirst cell subpack, the second cell subpack and the third cell subpack.14. An apparatus, comprising: multiple cells arranged in series, themultiple cells configured to provide a first voltage level to a firstload through a first voltage rail; a voltage regulator connected to thefirst voltage rail, wherein the voltage regulator is charged by themultiple cells in series; and at least one lithium ion cell connected toan output of the voltage regulator, the lithium ion cell having abattery chemistry different from the multiple cells arranged in series,wherein the voltage regulator is configured to charge the lithium ioncell.
 15. The apparatus of claim 14 wherein the lithium ion cell is alithium iron phosphate cell.
 16. The apparatus of claim 14 wherein thevoltage regulator is configured to charge the lithium ion cell only ondemand at peak efficiency.
 17. The apparatus of claim 14 wherein thelithium ion cell is configured to provide a second voltage level to atleast a second load through a second voltage rail.
 18. An apparatus,comprising: a first cell subpack comprising multiple matched cells inseries to provide a first voltage level; and a second cell subpackconnected in series to the first cell subpack, the second cell subpackcomprising multiple unmatched cells in parallel to provide a secondvoltage level, wherein the first voltage level is different from thesecond voltage level and the unmatched cells in parallel have a samecell chemistry.
 19. The apparatus of claim 18 wherein charge istransferred between the first cell subpack and the second cell subpackto recharge the second cell subpack from the first cell subpack.
 20. Theapparatus of claim 18 wherein the first cell subpack operatesindependent from the second cell subpack.